1. Field of the Invention
The present invention relates to an inorganic fiber mat, a holding sealer, a sound absorber and a method for manufacturing an inorganic fiber mat.
2. Discussion of the Background
Conventionally, a catalyst converter has been used as an exhaust gas purifying apparatus that purifies exhaust gases discharged from an internal combustion engine. The catalyst converter generally includes a holding sealer interposed between a catalyst supporting carrier (exhaust gas treatment unit) on which a catalyst is supported and a metallic shell (casing) that accommodates the catalyst supporting carrier. As the holding sealer, an inorganic fiber mat is sometimes employed which is made of ceramic fibers such as alumina-silica-based ones and that is impregnated with an organic binder and molded into a mat shape having a predetermined thickness.
In the catalyst converter, the holding sealer serves for thermal insulation, prevents leakage of unpurified exhaust gases through between the shell and the catalyst supporting carrier, and also prevents damage caused by contact between the shell and the catalyst supporting carrier.
Here, inorganic fibers that form the holding sealer (inorganic fiber mat) are fine fibers. Therefore, in assembling the catalyst converter, fibers may scatter away from a surface of the holding sealer to undesirably worsen working conditions.
In this respect, JP-A 2003-105658 discloses that, in an alumina fiber aggregate, scattering of alumina short fibers can be suppressed by controlling an average fiber diameter and a minimum fiber diameter to a specific range.
JP-A 2006-342774 discloses that the alumina fiber aggregate disclosed in Patent Document 1 is used as the holding sealer to thereby suppress an amount of scattering of inorganic fibers caused in assembling a catalyst converter. In addition, JP-A 2006-342774 discloses scattering of inorganic fibers can be suppressed also by increasing an amount of organic binder contained the holding sealer.
The contents of JP-A 2003-105658 and JP-A 2006-342774 are incorporated herein by reference in their entirety.